Limit ResizeProcessor memory consumption

[antonfirsov]

Prerequisites

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• I have provided test coverage for my change (where applicable)

Description

This PR fixes #642 by limiting the memory consumption of ResizeProcessor to a value defined in Configuration.WorkingBufferSizeHintInBytes. Instead of allocating the whole first pass buffer, a sliding window is implemented by ResizeWorker<T>. The height of the window is a multiple of the vertical kernel's maximum diameter depending on Configuration.WorkingBufferSizeHintInBytes.

The implementation is most likely very different from MagicScaler's one (haven't seen it's code). It was a goal to keep the changes under control, the new code is basically a refactor of the old one.

The optimization is visually explained in ResizeWorker.pptx:

Results

There is no regression in speed. (Actually, we are faster now for .NET 4.72 than before.)

The resizing of a 4000 x 4000 image to 300 x 300 has been memory profiled using JetBrains dotMemory. The resize operation has been executed 50 times in a single process.

Memory profile before the optimization

Timeline:

Typical snapshot:

Memory profile after the optimization

Timeline:

(The second peak has been only triggered because I made the snapshot. Can anyone explain this?)

Typical snapshot:

[codecov]

Codecov Report

Merging #888 into master will increase coverage by 0.04%.
The diff coverage is 89.83%.

@@            Coverage Diff             @@
##           master     #888      +/-   ##
==========================================
+ Coverage   88.98%   89.02%   +0.04%     
==========================================
  Files        1018     1024       +6     
  Lines       44537    44786     +249     
  Branches     3220     3230      +10     
==========================================
+ Hits        39632    39872     +240     
- Misses       4194     4202       +8     
- Partials      711      712       +1

Impacted Files	Coverage Δ
...ests/TestUtilities/ImageProviders/SolidProvider.cs	60% <ø> (ø)	⬆️
...nsforms/ResizeKernelMapTests.ReferenceKernelMap.cs	92.3% <0%> (ø)	⬆️
tests/ImageSharp.Tests/Memory/Buffer2DTests.cs	100% <100%> (ø)	⬆️
...PixelFormats/PixelConversionModifiersExtensions.cs	100% <100%> (ø)	⬆️
.../Attributes/WithBasicTestPatternImagesAttribute.cs	100% <100%> (ø)
...ng/Processors/Transforms/Resize/ResizeProcessor.cs	94.78% <100%> (-1.45%)	⬇️
...Tests/TestUtilities/ImageProviders/FileProvider.cs	57.81% <100%> (ø)	⬆️
...estUtilities/ImageProviders/TestPatternProvider.cs	98.01% <100%> (ø)	⬆️
...ng/Processors/Transforms/Resize/ResizeKernelMap.cs	94.73% <100%> (+0.05%)	⬆️
.../TestUtilities/ImageProviders/TestImageProvider.cs	84.78% <100%> (+0.33%)	⬆️
... and 28 more

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